I've found that it depends on the day. If my motivation has been low, sometimes going into the office can be just the kick in the pants I need. Other times, I just need to get out to a coffee shop to be in a more "public" setting.
On the other hand, there are definitely days when I know what needs done and I'm excited to do it – on days like those, people, meetings, and commutes only serve to get in the way of real work.